Arrangement for connecting or terminating coaxial conductors



Jan. 19, 1932. I

ARRANGEMENT FOR E- GREEN 1,841,473

CONNECTING OR TERMINATING COAXIAL CONDUCTORS Fi led Jan. 50, 1930bzsuldtzh 70 Spacer y (bpper wire or Braid.

INVENTOR EIG'weI/I/ ATTORNEY efiects. It is one of t ent invention toprovide arrangements w ere-' Patented Jan. 19, 1932 UNITED STATES PATENTOFFICE ESTILL I. GREEN, ,OF EAST ORANGE, NEW JERSEY, ASSIGNOR TOAMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORKARRANGEMENT FOB CONNECTING OR TERMINATING CO'AXIAL CONDUCTOR-SApplication filed January 30, 1930. Serial No. 424,677.

This invention relates to coaxial conductor systems, and moreparticularly to arrangements for connectin 'or terminatingcoaxialconductor systems of difierent sizes or dimensions without introducingimpedance irregularities.

Where it is desired to transmit a wide range of frequencies as, forexample, for television purposes or for providing a large number ofcarrier channels, it is advantageous to use a coaxial conductor system.Such a system may comprise an inner cylindrical conductor surrounded bya concentrically arranged hollow cylindrical conductor acting as areturn for the inner conductor, the two conductors being separatedpreferably by a dielectric which is largely gaseous.

In a system of this type, if the ratio of the inner diameter of theouter conductor to the outer diameter of the inner conductor is fixed,the attenuation of the conducting system varies inversely with thediameter. It is, therefore, desirable in using such a system to make themain line circuit of as large a diameter as is economically andphysically practicable in order that a low attenuation may be obtained,Occasions will frequently arise, however, in which it is desirable touse a part of the system a conductor arrangement of smaller diameterthan that employed for the normal line construction. Under theseconditions it is extremely advantageous to be able to match theimpedance of the two 00- axial circuits, thereby eliminating reflectione purposes of the resby this result may be attained.

The invention will now be more fully understood from the followingdescription, when read in connection with the accompanying drawings,Figures 1, 2 and 3 of which v illustrate difierent arrangements forinterconnecting coaxial conductor ferent types and dimensions.

Let us consider concentric conductor arran ents comprising an innercylindrical con uctor having an outer diameter b surrounded by a coaxialouter cylindrical conductor having an inner diameter 0, the two systemsofdifconductors bemg in proper concentric relation and out of electricalcontact with each other by means of spaced dielectric washers or thelike, preferably of small loss angle and low dielectric constant, sothatthe dielectric between the two conductors will be principally ofair. Ordinarily in the design of such a system the diameter of the outerconductor will be determined by physical conditions and may he treatedas fixed. The attenuation of the system for a given inner diameter ofthe outer conductor will then vary with different outer diameters of theinner conductor. By analogy tov formula page 109', of Calculation ofalternating current problems, by L. Cohen, the capacity of the structureherein considered will have the value.

log

in which K is the dielectric constant of the insulation between theconductors. Likewise from formula (56) on page 72 of the. Cohenpublication the high fre uenc inductance in abhenries per centimeter ast e value X 10' farads per mile (1) L=2log% 2 The high frequencyimpedance of the coaxial circuit is Substituting the values givenbyEquations (1) and (3) in Equation (4) we have z.-e0x i -x log. 3 .(6)

too

From Equation (6) it is evident that the impedance at high frequenciesis determined by the ratios of the diameters of the conductors for anygiven insulating material.

Now in an application of E. 1. Green, Serial No. 365,518, filed May 23,1929, entitled Concentric conductor transmission system, it is shownthat when the size of the outer conductor is fixed the attenuation willbe a minimum when the ratio for interconnecting concentric conductorsections of different dimensions without introducing impedanceirregularities. This is done by so designing the two sections which areto be oined that regardless of their actual diameters the ratio is thesame for both where the same dielectric material is employed.

There are various conditions under which a change in diameter in acoaxial system may be necessary or desirable. For ordinary constructionthe diameter of the outer conductor may be determined by the fact thatit must enter the opening of a conduit or pass through the bridle ringof an overhead cable system. When entering an ofiice, however, aconcentric conductor system of smaller diameter may be very useful. Infact a flexible coaxial construction perhaps provided with solidinsulation between conductors,-might be desirable. Also, for long spansover rivers a conductor of large diameter might be disadvantageous and aconcentric conductor section of smaller diameter could be employed. Forshort submarine stretches under rivers, a form of construction somewhatdiiferent from that normally employed would be necessary. Smallerconductors, probably stranded, and separated by solid insulation woulddoubtless be required in this instance. For certain types of ductconstructions in cities or towns it might be necessary to introduce aconcentric conductor section of smaller diameter. Andfinally,foremergency construction where a portion of the regularconductor system is out of order, a flexible form of con struction wouldbe desirable for use in bridging around the line sections under repair.

In any of the foregoing cases a perfect impedance match at highfrequencies can be obtained by using a proper diameter ratio for the twocircuits which are to be joined. If air insulation is employed betweenconductors in both circuits or if the same solid insulation is employedin both circuits, the diameter ratios will be the same for both. The useof solid insulation between the conductors of one circuit and airinsulation for the connecting circuit would necessitate dilferentdiameter ratios for the two circuits. The correct diameter ratio whenusing solid insulation of dielectric constant K for one circuit and airinsulation for the other would be I 1/]? %=[%l where is the diameterratio'for the circuit employing the solid insulation, and

is the diameter ratio for the circuit with air insulation. "When theinsulating medium is not uniform, the value of K should be the weightedaverage dielectric constant for the different insulating materialsemployed. When different types of solid insulation are employed for thetwo circuits the correct diameter ratios are given by the expression:

is the diameter ratio for the circuit employing insulation of thedielectric constant K and where ductors being separated by s aceddielectric washers 14. The concentric system thus formed is to beconnected to a similar concentric system of smaller conductorscomprising an inner conductor 12 surrounded by an outer conductor 10',these two conductors being separated by spaced insulating washers 14.Assuming that the diameter ratios are properly determined in accordancewith Equation (7), the physical connections between the two sections maybe made by employing unions .16 and 18 of shouldered construction, eachunion having its flanges secured to the corresponding conductors asshown.

Instead of employing shouldered flanges as in Fig. 1, the flanges may betapered as illustrated in Fig. 2. I,

Fig. 3 shows an arrangement which may be employed where a concentricconductor'system employing substantially air dielectric is connected toaconducting system in which the insulation between the conductors is ofsolid material. For example, the latter conductor system is shown ascomprising an inner conductor 12' surrounded by a braided copperconductor 10' which is insulated from the inner conductor by a solidmass of insulation 14'. Also the outer conductor may be covered by somesolid insulating material such as 22. The outer dielectric doesnotaffect the impedance of the conducting system, however, as the current,due to the skineflect, flows in the inner surface of the outer conductorand the outer surface of the inner conductor and there is substantiallyno electric or magnetic field extending into the space surrounding theouter conductor. To effect the junction the system comprising conductors10 and 12 may have the endof the smaller cable 1012 inserted in the oening of the conductor 10 and sealed thereto by means of a terminal plugor seal 20. The inner conductor 12 is then tied to the inner conductor12 by means of wires 18, and the outer conductor 10' is connected to theouter conductor 10 by means of. wires 16. Here again the design of theconductor system 10-1214 may be readily determined from formula (7),assuming that K is the dielectric constant of the insulating material ofthe smallerconductor system while the dielectric constant of the spacebetween the conductors 10 and 12 is not materially diflerent from thatof air.

It will be obvious that the general principles herein disclosed may beembodied in many other organizations widely difi'erent from thoseillustrated without de arting from the s irit of the invention as deflned in the following claims.

What is claimed is:

1. In a transmission system, two concentric conductor sections eachcomprising inner and outer c lindrical conductors coaxisections being ofdifferent diameters but said sections being so designed as to havesubstantially the same characteristic impedance, and means forinterconnecting said sections.

2. In a transmission system, two concentric conductor sections eachcomprising inner and outer cylindrical conductors coaxially arranged,the outer conductors of the sections being of different diameters butthe ratio of the inner diameter of the outer conductor to the outerdiameter of the inner con- .ductor of the one section being so relatedto the corresponding ratio for the other section that each section hassubstantially the same characteristic impedance, and means forinterconnecting said sections.

3. In a transmission system, two concentric conductor sections eachcomprising inner and outer cylindrical conductors coaxially arranged,the outer conductors of the sections being of different diameters butthe ratio ofthe inner diameter of the outer conductor to the outerdiameter of the inner conductor being substantially the same for bothsections, and means for interconnecting said sections.

4. In a transmission system, two concentric conductor sections eachcomprising inner and outer cylindrical conductors coaxially arranged,the outer conductors of the sections being of different diameters, theconductors of one section being separated by a substantially gaseousdielectric and the conductors of the other section being separated byinsulation having a dielectric constant different from that of air, thediameters of the conductors of the two sections being related by theformula when 0 is the inner diameter of the outer conductor and Z) theouter diameter of the inner conductor of one section, 0 and b areJanuary, 1930.

. ESTILL I. GREEN.

ally arranged, t e outer conductowhe

